U.S. patent number 8,816,015 [Application Number 13/832,502] was granted by the patent office on 2014-08-26 for low emission polyoxymethylene.
This patent grant is currently assigned to Ticona, LLC. The grantee listed for this patent is Ticona LLC. Invention is credited to Robert Gronner, Rong Luo, Nicolai Papke, Xinyu Zhao.
United States Patent |
8,816,015 |
Luo , et al. |
August 26, 2014 |
**Please see images for:
( Certificate of Correction ) ** |
Low emission polyoxymethylene
Abstract
Low VOC emission polyoxymethylene and compositions and products
that incorporate the polyoxymethylene are described. The
polyoxymethylene is end capped with compound that can prevent
degradation of the polymer and subsequent emission of VOC
degradation products such as formaldehyde. The end-capped
polyoxymethylene can include an inorganic linkage within the
polymer backbone that is the reaction product of a terminal
hydroxyl group of the polyoxymethylene and a hydrolyzable group of
the compound. Also disclosed are products as may be formed from the
low VOC emission polyoxymethylene.
Inventors: |
Luo; Rong (Florence, KY),
Zhao; Xinyu (Cincinnati, OH), Gronner; Robert
(Earlanger, KY), Papke; Nicolai (Mainz-Kastel,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Ticona LLC |
Florence |
KY |
US |
|
|
Assignee: |
Ticona, LLC (Florence,
KY)
|
Family
ID: |
49671023 |
Appl.
No.: |
13/832,502 |
Filed: |
March 15, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130324675 A1 |
Dec 5, 2013 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61655685 |
Jun 5, 2012 |
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Current U.S.
Class: |
525/398;
435/6.14; 435/287.2 |
Current CPC
Class: |
C08L
83/08 (20130101); C08G 6/00 (20130101); C08G
77/382 (20130101) |
Current International
Class: |
C08G
64/00 (20060101); C08G 63/02 (20060101) |
Field of
Search: |
;525/398
;435/6.14,287.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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62-181305 |
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Aug 1987 |
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JP |
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09-235446 |
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Sep 1997 |
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JP |
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2000-230026 |
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Aug 2000 |
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JP |
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2007-051253 |
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Mar 2007 |
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JP |
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2009-132824 |
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Jun 2009 |
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JP |
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2010-144155 |
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Jul 2010 |
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JP |
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WO 01/23473 |
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Apr 2001 |
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WO |
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Other References
International Search Report and Written Opinion for
PCT/US2013/403254 dated Jul. 17, 2013. cited by applicant.
|
Primary Examiner: Boykin; Terressa
Attorney, Agent or Firm: Dority & Manning, P.A.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
The present application claims filing benefit of U.S. Provisional
Patent Application Ser. No. 61/655,685 having a filing date of Jun.
5, 2012, which is incorporated herein in its entirety.
Claims
What is claimed is:
1. An end-capped polyoxymethylene, the end-capped polyoxymethylene
comprising an inorganic linkage to a non-hydrolyzable organic
group, the non-hydrolyzable organic group being at the terminus of
the end-capped polyoxymethylene, the end-capped polyoxymethylene
being the reaction product of a hydrolyzable group of an end
capping compound and a terminal hydroxy group of a polyoxymethylene
homopolymer or copolymer, the end capping compound having the
general structure of: (R.sub.6).sub.qAX.sub.(4-q)wherein A is an
inorganic atom that forms the inorganic linkage, q is 1 to 3, X is
the hydrolyzable group, and R.sub.6 is the nonhydrolyzable organic
group.
2. The end-capped polyoxymethylene according to claim 1, wherein
the inorganic linkage is a siloxane linkage.
3. The end-capped polyoxymethylene according to claim 1, wherein
the copolymer includes less than about 1% by weight of the
copolymer monomer units having at least two adjacent carbon
atoms.
4. The end-capped polyoxymethylene according to claim 1, wherein
the nonhydrolyzable organic group comprises a non-reactive terminus
or comprises reactive functionality at the terminus.
5. The end-capped polyoxymethylene according to claim 4, wherein
the nonhydrolyzable organic group comprises reactive functionality
at the terminus selected from halogen, vinyl, epoxy, amino,
mercapto, or combinations thereof.
6. The end-capped polyoxymethylene according to claim 1, wherein
the polyoxymethylene comprises less than about 2% low molecular
weight constituents,
7. The end-capped polyoxymethylene according to claim 1, the
end-capped polyoxymethylene having a melt flow index of greater
than about 5 grams per 10 minutes and a comonomer content of less
than about 1% by weight of monomer units having two or more
adjacent carbon atoms, the polyoxymethylene having a hydrolyzable
content of less than about 0.9 weight percent.
8. The end-capped polyoxymethylene according to claim 1, the
end-capped polyoxymethylene having a melt flow index of greater
than about 5 grams per 10 minutes and a comonomer content of
greater than about 1% by weight of monomer units having two or more
adjacent carbon atoms, the end-capped polyoxymethylene having a
hydrolyzable content of less than about 0.23 weight percent.
9. The end-capped polyoxymethylene according to claim 1, the
end-capped polyoxymethylene having a melt flow index of greater
than about 5 grams per 10 minutes, the end-capped polyoxymethylene
having a hydrolyzable content of less than about 3mmol/kg.
10. The end-capped polyoxymethylene according to claim 1, the
end-capped polyoxymethylene having a melt flow index of less than
about 5 grams per 10 minutes and a hydrolyzable content of less
than about 5 weight percent or less than about 5 mmol/kg.
11. A polymeric composition comprising the end-capped
polyoxymethylene according to claim 1.
12. The polymeric composition according to claim 11, wherein the
end-capped polyoxymethylene has a melt flow index of greater than
about 5 grams per 10 minutes, the polymeric composition exhibiting
a formaldehyde emission level of less than about 3 ppm as
determined according to VDA-275.
13. The polymeric composition according to claim 11, wherein the
polyoxymethylene has a melt flow index of less than about 5 grams
per 10 minutes, the polymeric composition exhibiting a formaldehyde
emission level of less than about 7.5 ppm as determined according
to VDA-275.
14. The polymeric composition according to claim 11, the polymeric
composition further comprising a formaldehyde scavenger, the
polymeric composition exhibiting a formaldehyde emission level of
less than about 3 ppm as determined according to VDA-275.
15. The polymeric composition according to claim 11, the polymeric
composition further comprising an acid scavenger.
16. The polymeric composition according to claim 15, wherein the
acid scavenger is a hydroxide, inorganic acid salt, phosphate,
hydrogen phosphate, or carboxylic acid salts of alkali metals or
alkaline earth metals.
17. A shaped article comprising the polymeric composition according
to claim 11.
18. The shaped article according to claim 17, wherein the shaped
article is a mechanical gear, a sliding or guiding element, a
housing part, a spring, a chain, a screw, a nut, a fan wheel, a
pump part, a valve body, a lock, a handle, a hinge, or a
zipper.
19. The shaped article according to claim 18, wherein the shaped
article is a component of an electronic device, a medical device, a
sporting good, an automotive component, or a household
appliance.
20. The shaped article according to claim 19, wherein the
automotive component is a fuel system component, a lighting or
signaling component, or a window or door lock system component.
21. A method for reducing volatile organic compound emissions from
a polymeric composition, the method comprising combining a
polyoxymethylene with an end-capping compound, wherein the
polyoxymethylene and the end-capping compound are combined in a
melt, the end-capping compound having the following structure:
(R.sub.6).sub.qAX.sub.(4-q)wherein A is an inorganic atom, q is 1
to 3, X is a hydrolyzable group, and R.sub.6 is a nonhydrolyzable
organic group the polyoxymethylene comprising a terminal hydroxyl
group, the hydrolyzable group of the end-capping compound reacting
with a terminal hydroxyl group of the polyoxymethylene to form an
end-capped polyoxymethylene, the end capped polyoxymethylene
including the inorganic atom as an inorganic linkage in the polymer
chain.
22. The method according to claim 21, wherein the end-capping
compound is a silane compound.
23. The method according to claim 21, wherein the end-capping
compound is provided in an amount of less than about 5 wt. % by
weight of the polyoxymethylene.
24. The method according to claim 21, further comprising combining
an additive with the end-capped polyoxymethylene.
25. The method according to claim 24, wherein the additive is an
acid scavenger.
26. The method according to claim 21, further comprising shaping
the polymeric composition comprising the end-capped
polyoxymethylene to form a product.
Description
BACKGROUND OF THE INVENTION
Oxymethylene polymers (also referred to as polyoxymethylenes and
polyacetals) are a class of thermoplastics that have been found
useful for a variety of applications including automotive
construction, electrical applications, and medical technologies.
Polyoxymethylenes have excellent properties including mechanical
(e.g., strength) characteristics, permeability resistance, fatigue
resistance, abrasion resistance, chemical resistance, and
moldability.
Unfortunately, polyoxymethylenes tend to degrade when heated and
are unstable, particularly in an oxidative, basic, or acidic
environment. Moreover, as the polymers degrade they emit
degradation products such as formaldehyde as volatile organic
compounds (VOCs). Formaldehyde as well as other VOC emissions lead
to an unpleasant odor and can raise environmental health concerns.
The emission of VOCs and particularly the emission of formaldehyde
by polyoxymethylenes both during processing and after the polymer
has been molded into a desired shape have been problematic for the
industry and has impaired the usefulness of these materials in many
application sectors. For instance, the automotive industry has
developed analysis methods (see, e.g., German Automotive Industry
Recommendation No. 275, documented by Kraftfahrwesen e.V., July,
1994) for determining formaldehyde emission from polyoxymethylene
components and strongly encourages the development of low emission
polyoxymethylene polymers.
In an attempt to limit the VOC emissions of oxymethylene polymers,
a variety of polymer stabilizers have been developed. For instance
nitrogen-containing compounds such as dicyandiamide and
amino-substituted triazine compounds have been utilized as polymer
stabilizers. These stabilizers generally function as formaldehyde
scavengers to bind formaldehyde and prevent emission.
Unfortunately, such stabilizers do nothing to prevent the
degradation of the polyoxymethylene polymers that leads to the
formaldehyde emission in the first place. In addition, as
stabilizers are not bound to the oxymethylene polymer, they have a
tendency to migrate to the surface of the formed products and cause
deposits and surface imperfections on the products.
What is needed in the art are polyoxymethylenes that are resistant
to degradation, so as to provide polymers, polymer compositions,
and products formed from the polymers that exhibit low VOC
emission, have little or no mold deposits and improved surface
characterization, present desirable strength and resistance
characteristics, and are suitable for use in a variety of
applications.
SUMMARY OF THE INVENTION
Disclosed are end-capped polyoxymethylenes that include an
inorganic linkage to a non-hydrolyzable organic radical at the
terminus of the end-capped polymer. Also disclosed are compositions
and products including the end-capped polyoxymethylenes. The
compositions can exhibit very low VOC emission. For instance, a
polyoxymethylene composition including a low to mid-molecular
weight end capped polyoxymethylene (e.g., having a melt flow index
of greater than about 5 g/10 min) can have a formaldehyde emission
of less than about 3 ppm as determined according to VDA-275. A
composition including high molecular weight end capped
polyoxymethylene (e.g., having a melt flow index of less than about
5 g/10 min) can have a formaldehyde emission level of less than
about 7.75 ppm as determined according to VDA-275.
A composition including the end-capped polyoxymethylenes can
beneficially be utilized in forming products such as, without
limitation, automotive components such as fuel system components
(e.g., fuel tanks, fuel sender unit, fuel caps, fuel pumps, etc.),
lighting and signal components, window and door lock system
components, and so forth; electrical components such as insulators,
connectors, etc.; medical components such as inhalers and injection
pens; sporting goods; and household appliances.
Also disclosed are methods for reducing the VOC emissions from a
polyoxymethylene composition. For example, a method can include
combining a polyoxymethylene with a compound, the compound
comprising an inorganic atom, a hydrolyzable group and a
nonhydrolyzable group. The hydrolyzable group can react with a
terminal hydroxyl group of the polyoxymethylene to form an
end-capped polyoxymethylene. The end-capped polyoxymethylene
includes an inorganic linkage to a non-hydrolyzable organic radical
at the terminus of the end-capped polymer that is formed upon
reaction of terminal hydroxyl groups of the polyoxymethylene with
the compound.
BRIEF DESCRIPTION OF THE FIGURES
The present disclosure may be better understood with reference to
the following figures:
FIG. 1 illustrates a comparison of the hydrolyzable content of a
composition including an end-capped polyoxymethylene as described
herein, and two comparative compositions.
FIG. 2 illustrates the results of a thermogravimetric analysis of
the compositions of FIG. 1 at a first set of testing
conditions.
FIG. 3 illustrates the results of a thermogravimetric analysis of
the compositions of FIG. 1 at a second set of testing
conditions.
FIG. 4 illustrates a comparison of the hydrolyzable content of a
composition including another end-capped polyoxymethylene as
described herein, and a comparative composition.
FIG. 5A and FIG. 5B are images of a comparative sample
polyoxymethylene composition showing a mold deposit in the
ventilation channel.
FIG. 6A and FIG. 6B are images of an inventive sample
polyoxymethylene composition showing a very thin mold deposit on
the ring channel, but it could not be transferred for
identification.
FIG. 7A and FIG. 7B are images of an inventive sample
polyoxymethylene composition with no mold deposit found on the
sample.
FIG. 8 illustrates a comparison of the hydrolyzable content of a
composition including another end-capped polyoxymethylene as
described herein, and two comparative compositions.
FIG. 9 presents the formaldehyde emission levels with melt
temperature for several samples as described herein.
FIG. 10 presents the change in Gardner Yellowness Index with melt
temperature for several samples as described herein.
FIG. 11 presents the formaldehyde emission levels with melt
temperature for two samples as described herein.
FIG. 12 presents the formaldehyde emission levels with melt
temperature for two samples as described herein.
DETAILED DESCRIPTION
It is to be understood by one of ordinary skill in the art that the
present discussion is a description of exemplary embodiments only,
and is not intended as limiting the broader aspects of the present
disclosure.
The present disclosure is generally directed to a low VOC emission
polyoxymethylene and compositions and products that incorporate the
polyoxymethylene. More specifically, the polyoxymethylene is end
capped with a compound that includes an inorganic atom, a
hydrolyzable group and a non-hydrolyzable group. Following capping
of the polymer, the polymer can include an inorganic linkage to the
non-hydrolyzable group at the polymer terminus following the
reaction of a terminal hydroxyl group of the polyoxymethylene and
the hydrolyzable group of the compound. The end capping group on
the terminus of the polyoxymethylene can prevent degradation of the
polymer and subsequent emission of VOC degradation products such as
formaldehyde.
Any polyoxymethylene, i.e., either copolymers or homopolymers, can
be end capped so as to form the low-emission polyoxymethylene.
Beneficially, the polyoxymethylene can be formed to exhibit
particular qualities, such as a particular melt flow index,
mechanical characteristics, thermal characteristics, etc. according
to standard practice, and the addition of the end cap to the
polymer can lower the VOC emission characteristics with little or
no effect on the other characteristics of the polymer. For
instance, the melt flow index, tensile strength characteristics,
modulus characteristics, etc., will be retained following end
capping of the polymer, which can simplify formation processes.
The addition of the end capping group to the polyoxymethylene can
decrease the VOC emission as compared to a non-capped polymer. For
instance, a composition including a low to mid-molecular weight end
capped polyoxymethylene polymer having a melt flow index of greater
than about 5 grams per 10 minutes (g/10 min) as determined
according to ISO Test Method No. 1133 at 190.degree. C. and 2.16
kg, can have a formaldehyde emission level of less than about 3
ppm, less than about 1.60 ppm, less than about 1.5 ppm, less than
about 1.0 ppm, or less than about 0.5 ppm as determined according
to VDA-275. When considering a composition including a high
molecular weight polyoxymethylene, for instance having a melt flow
index of less than about 5 g/10 min as determined according to ISO
1133 at 190.degree. C. and 2.16 kg, the composition can have a
formaldehyde emission level of less than about 7.5 ppm, less than
about 6.0 ppm, or less than about 5.5 ppm, as determined according
to VDA-275.
The end capped polyoxymethylenes can also exhibit a low
hydrolyzable content, which is a measure of the terminal
hydroxyl-containing groups such as terminal hemiacetals that can be
degraded to form VOCs. For instance, low to mid molecular weight
end capped polyoxymethylene having a melt flow index of greater
than about 5 grams per 10 minutes (g/10 min) as determined
according to ISO Test Method No. 1133 at 190.degree. C. and 2.16
kg, having a relatively low comonomer content (e.g., less than
about 1%, or less than about 0.1% by weight of monomer units having
two or more adjacent carbon atoms) can have a hydrolyzable content
of less than about 0.9 wt. %, less than about 0.8 wt. %, or less
than about 0.7 wt. % as determined by a sulfite titration method. A
low to mid-molecular weight end capped polyoxymethylene having a
relatively high comonomer content (e.g., greater than about 1% by
weight of monomer units having two or more adjacent carbon atoms)
can have a hydrolyzable content of less than about 0.23 wt. %, less
than about 0.22 wt. %, or less than about 0.21%. For instance, a
low to mid-molecular weight end capped polyoxymethylene can have a
hydrolyzable content of less than about 3 mmol/kg, or less than
about 2.5 mmol/kg.
A high molecular weight end capped polyoxymethylene having a melt
flow index of less than about 5 grams per 10 minutes (g/10 min) as
determined according to ISO Test Method No. 1133 at 190.degree. C.
and 2.16 kg can have a hydrolyzable content of less than about 5
wt. %, less than about 4 wt. %, or less than about 3 wt. % as
determined by a sulfite titration method. In one embodiment, a high
molecular weight end capped polyoxymethylene can have a
hydrolyzable content of less than about 5 mmol/kg, or less than
about 3 mmol/kg.
Moreover, as a composition including the end capped
polyoxymethylene can incorporate little or no traditional
stabilizing agents, a product that incorporates the composition can
exhibit decreased mold deposit and surface imperfections due to
migration of a stabilizing agent.
In addition to the above, the end capping of the polyoxymethylene
by use of the compound can prevent discoloration of the polymer
composition. While not wishing to be bound to any particular
theory, it is believed that the prevention of polymer degradation
due to the presence of the terminal cap and the related prevention
of degradation products within the composition can prevent
discoloration. The variation in discoloration between a composition
including the end capped polyoxymethylene and a similar
polyoxymethylene that is not end capped can be quantified by
measuring absorbance with an optical reader in accordance with a
standard test methodology known as "CIELAB", which is described in
Pocket Guide to Digital Printing by F. Cost, Delmar Publishers,
Albany, N.Y. ISBN 0-8273-7592-1 at pages 144 and 145 and
"Photoelectric color difference meter", Journal of Optical Society
of America, volume 48, page numbers 985-995, S. Hunter, (1958),
both of which are incorporated herein by reference in their
entirety.
The CIELAB test method defines three "Hunter" scale values, L*, a*,
and b*, which correspond to three characteristics of a perceived
color based on the opponent theory of color perception and are
defined as follows:
L=Lightness (or luminosity), ranging from 0 to 100, where 0=dark
and 100=light;
a=Red/green axis, ranging from -100 to 100; positive values are
reddish and negative values are greenish; and
b=Yellow/blue axis, ranging from -100 to 100; positive values are
yellowish and negative values are bluish.
Color measurement can be performed using a DataColor 650
Spectrophotometer utilizing an integrating sphere with measurements
made using the specular included mode. Color coordinates can
likewise be calculated according to ASTM D2244-11 under an
illuminant D65/10.degree., A/10.degree., or F2/10.degree. observer,
using CIELAB units. For example, the polymer composition can
exhibit an `L` value between about 85 and about 95, for instance
between about 87 and about 94; an `a` value between about -0.7 and
about 0.5, for instance between about -0.6 and about 0.3; and a `b`
value between about -0.5 and about 2, for instance between about
-0.3 and about 1.7.
The polymer composition can also exhibit a relatively low
yellowness index, which is another format for determining the lack
of discoloration of the polymer composition. For example, the
polymer composition can exhibit a Gardner Yellowness Index as
determined according to ASTM E313. For example, the polymer
composition can exhibit a Gardner Yellowness Index at 185.degree.
C. of less than about -6, or less than about -5. At higher
temperatures, the Gardner Yellowness index can increase somewhat,
but still present good color characteristics. For instance, at
205.degree. C., the polymer composition can exhibit a Gardner
Yellowness Index of less than zero, for instance less than about
-1, less than about -2, or less than about -3. At 220.degree. C.,
the polymer composition can exhibit a Gardner Yellowness Index of
less than about 2, less than about 1, or less than about -1, in one
embodiment.
The polyoxymethylene can be either an oxymethylene homopolymer or
copolymer and is not limited as to any particular monomeric
components or relative amounts of monomeric components. For
instance, the polyoxymethylene can be a conventional oxymethylene
homopolymer and/or oxymethylene copolymer. Conventional
polyoxymethylenes are generally unbranched linear polymers that
contain greater than about 80%, or greater than about 90%,
oxymethylene units (--CH.sub.2O--). The polyoxymethylene is not
limited to this level of oxymethylene units, however, and polymers
including lower content of oxymethylene units are also encompassed
herein. According to one embodiment, the polyoxymethylene can be a
homo- or copolymer which comprises greater than about 50 mol %,
greater than about 75 mol %, greater than about 90 mol %, or
greater than about 95 mol % --CH.sub.2O-- repeat units.
Polyoxymethylenes encompass both homopolymers of formaldehyde or
its cyclic oligomers, such as trioxane or
1,3,5,7-tetraoxacyclooctane, and corresponding copolymers. By way
of example, the following components can be used in any suitable
proportional relationship in the polymerization process:
ethyleneoxide, 1,2-propyleneoxide, 1,2-butyleneoxide,
1,3-butyleneoxide, 1,3-dioxane, 1,3-dioxolane, 1,3-dioxepane and
1,3,6-trioxocane as cyclic ethers as well as linear oligo- or
polyformals, like polydioxolane or polydioxepane. Further,
conventional functionalized polyoxymethylenes that are prepared by
copolymerization of trioxane and the formal of trimethylolpropane
(ester), of trioxane and the .alpha.,.alpha.- and the
.alpha.,.beta.-isomers of glyceryl formal (ester) or of trioxane
and the formal of 1,2,6-hexantriol (ester) can be used as the
polyoxymethylene. An oxymethylene copolymer can generally include
greater than about 0.1% by weight of monomer units of the copolymer
having at least two adjacent carbon atoms. By way of example, an
oxymethylene copolymer can include from about 1% to about 10% by
weight of monomer units having two or more adjacent carbon atoms.
Such conventional oxymethylene homo- or copolymers are known to the
person skilled in the art and are described in the literature.
In one embodiment, an oxymethylene copolymer can include up to
about 50 mol %, for instance from about 0.1 mol % to about 20 mol
%, or from about 0.3 mol % to about 10 mol %, of repeat units
having the following structure:
##STR00001## wherein
R.sub.1 to R.sub.4, independently of one another, are hydrogen,
alkyl, or halogen-substituted alkyl having from 1 to 4 carbon
atoms,
R.sub.5 is --CH.sub.2--, --CH.sub.2O--, C1-C4-alkyl- or
C1-C4-haloalkyl-substituted methylene, or a corresponding
oxymethylene group, and
n is from 0 to 3.
These groups may be introduced into the copolymers by the
ring-opening of cyclic ethers. Cyclic ethers can include those of
the formula:
##STR00002## where R.sup.1 to R.sup.5 and n are as defined
above.
Cyclic ethers which may be mentioned as examples are ethylene
oxide, propylene 1,2-oxide, butylene 1,2-oxide, butylene 1,3-oxide,
1,3-dioxane, 1,3-dioxolane, and 1,3-dioxepan, and comonomers which
may be mentioned as examples are linear oligo- or polyformals, such
as polydioxolane or polydioxepane.
Use can also be made of oxymethylene terpolymers, for example those
prepared by reacting trioxane with one of the abovementioned cyclic
ethers and with a third monomer, for instance a bifunctional
compound of the formula
##STR00003## where
Z is a chemical bond, --O-- or --ORO--(R.dbd.C1-C8-alkylene or
C2-C8-cycloalkylene).
Monomers of this type can include, without limitation, ethylene
diglycide, diglycidyl ether, and diethers composed of glycidyl
units and formaldehyde, dioxane, or trioxane in a molar ratio of
2:1, and also diethers composed of 2 mol of glycidyl compound and 1
mol of an aliphatic diol having from 2 to 8 carbon atoms, for
example the diglycidyl ethers of ethylene glycol, 1,4-butanediol,
1,3-butanediol, 1,3-cyclobutanediol, 1,2-propanediol, or
1,4-cyclohexene dial, to mention just a few examples.
The polyoxymethylene polymer can have a high content of terminal
hydroxyl groups including, for example, hydroxyethylene groups
(--OCH.sub.2CH.sub.2OH) and hemi-acetal groups (--OCH.sub.2OH). In
one embodiment, the terminal hydroxyl groups can be primarily
terminal hydroxyethylene groups. The polyoxymethylene can have, for
instance, greater than about 50%, greater than about 70%, greater
than about 75%, greater than about 85%, or greater than about 90%
terminal hydroxyl groups. In one embodiment, the polyoxymethylene
can have a content of terminal hydroxyl groups of greater than
about 5 mmol/kg, greater than about 10 mmol/kg, or greater than
about 15 mmol/kg, for example ranging from about 18 to about 40
mmol/kg, or from about 20 to about 30 mmol/kg. As utilized herein,
the term "terminal hydroxyl groups" refers to terminal groups at
any point of the polymer, including terminal side groups of the
main polymer backbone. The content of terminal hydroxyl groups can
be determined according to known practice, for instance as
described in K. Kawaguchi, E. Masuda, Y. Tajima, Journal of Applied
Polymer Science, Vol. 107, 667-673 (2008).
In addition to terminal hydroxyl groups, the polyoxymethylene may
also have other terminal groups usual for these polymers. Examples
of these are alkoxy groups, formate groups, acetate groups and
aldehyde groups.
The polyoxymethylene can be a low, mid- or high molecular weight
polyoxymethylene. In one embodiment, the polyoxymethylene can have
a melt flow index (MFI) ranging from about 1 to about 30 g/10 min,
as determined according to ISO 1133 at 190.degree. C. and 2.16 kg,
though polyoxymethylenes having a higher or lower melt flow index
are also encompassed herein. For example, the polyoxymethylene
polymer may be a low or mid-molecular weight polyoxymethylene that
has a melt flow index of greater than about 5 g/10 min, greater
than about 10 g/10 min, or greater than about 15 g/10 min. The melt
flow index of the polyoxymethylene polymer can be less than about
25 g/10 min, less than about 20 g/10 min, less than about 18 g/10
min, less than about 15 g/10 min, less than about 13 g/10 min, or
less than about 12 g/10 min. The polyoxymethylene polymer may for
instance be a high molecular weight polyoxymethylene that has a
melt flow index of less than about 5 g/10 min, less than about 3
g/10 min, or less than about 2 g/10 min.
The polyoxymethylene can have constituents of various molecular
weights. In one embodiment, the polyoxymethylene can have little or
no low molecular weight constituents. For instance, the
polyoxymethylene can have low molecular weight constituents (e.g.,
constituents having molecular weights below about 10,000 Dalton) of
less than about 15% by weight, less than about 10% by weight, less
than about 5% by weight, less than about 3% by weight, or less than
about 2% by weight, based on the total weight of the
polyoxymethylene.
The preparation of the polyoxymethylene can be carried out by
polymerization of polyoxymethylene-forming monomers, such as
trioxane or a mixture of trioxane and dioxolane and/or butanediol
formal in the presence of a molecular weight regulator such as
ethylene glycol or methylal. The polymerization can be effected as
precipitation polymerization or in the melt. Initiators which may
be used are the compounds known per se, including either anionic or
cationic initiators such as trifluoromethane sulfonic acid; these
can be added as solution in ethylene glycol to the monomer. By way
of example, a polyoxymethylene homopolymers can be formed via
anionic polymerization according to known methods. The procedure
and termination of the polymerization and working-up of the product
obtained can be carried out according to known processes. By a
suitable choice of the polymerization parameters, such as duration
of polymerization and/or amount of molecular weight regulator, the
molecular weight and hence the melt flow index value of the
resulting polymer can be adjusted. The criteria for choice in this
respect are known to the person skilled in the art. The
above-described procedure for the polymerization leads as a rule to
polymers having comparatively small proportions of low molecular
weight constituents. If a further reduction in the content of low
molecular weight constituents were to be desired or required, this
can be affected by separating off the low molecular weight
fractions of the polymer after the deactivation and the degradation
of the unstable fractions after treatment with a basic protic
solvent. This may be a fractional precipitation from a solution of
the stabilized polymer, polymer fractions of different molecular
weight distribution being obtained.
In one embodiment, a polyoxymethylene with hydroxyl terminal groups
can be produced using a cationic polymerization process, optionally
followed by solution hydrolysis to remove any unstable end groups.
Cationic initiators as are generally known in the art can be
utilized such as Lewis acids, and in one particular embodiment,
boron trifluoride. In one embodiment, however, the solution
hydrolysis process need not be carried out, as the end capping of
the polyoxymethylene with the compound can stabilize the as-formed
polymer. During cationic polymerization, a glycol, such as ethylene
glycol can be used as a chain terminating agent. The cationic
polymerization results in a bimodal molecular weight distribution
containing low molecular weight constituents.
According to one formation process, the polyoxymethylene forming
monomers can be polymerized in the presence of one or more
heteropolyacids. It has been discovered that the low molecular
weight constituents can be significantly reduced by conducting the
polymerization using a heteropolyacid such as phosphotungstic acid
as the catalyst. When using a heteropolyacid as the catalyst, for
instance, the amount of low molecular weight constituents can be
less than 2% by weight.
The term "heteropolyacid" is a generic term for a polyacid formed
by the condensation of different kinds of oxo acids through
dehydration. A heteropolyacid contains a mono- or poly-nuclear
complex ion wherein a hetero element is present in the center and
the oxo acid residues are condensed through oxygen atoms. Such a
heteropolyacid is represented by the formula:
H.sub.x[M.sub.mM'.sub.pO.sub.z]yH.sub.2O wherein
M represents an element selected from the group consisting of P,
Si, Ge, Sn, As, Sb, U, Mn, Re, Cu, Ni, Ti, Co, Fe, Cr, Th and
Ce,
M' represents an element selected from the group consisting of W,
Mo, V and Nb,
m is 1 to 10,
p is 6 to 40,
z is 10 to 100,
x is an integer of 1 or above, and
y is 0 to 50.
The central element (M) in the formula described above may be
composed of one or more kinds of elements selected from P and Si
and the coordinate element (M') is composed of at least one element
selected from W, Mo and V.
Specific examples of heteropolyacids include those selected from
the group consisting of phosphomolybdic acid, phosphotungstic acid,
phosphomolybdotungstic acid, phosphomolybdovanadic acid,
phosphomolybdotungstovanadic acid, phosphotungstovanadic acid,
silicotungstic acid, silicomolybdic acid, silicomolybdotungstic
acid, silicomolybdotungstovanadic acid and acid salts thereof.
The heteropolyacid may be dissolved in an alkyl ester of a
polybasic carboxylic acid. It has been found that alkyl esters of
polybasic carboxylic acid are effective to dissolve the
heteropolyacids or salts thereof at room temperature (25.degree.
C.).
Examples of the alkyl ester of a polybasic carboxylic acid can
include, but are not limited to, dimethyl glutaric acid, dimethyl
adipic acid, dimethyl pimelic acid, dimethyl suberic acid, diethyl
glutaric acid, diethyl adipic acid, diethyl pimelic acid, diethyl
suberic acid, diemethyl phthalic acid, dimethyl isophthalic acid,
dimethyl terephthalic acid, diethyl phthalic acid, diethyl
isophthalic acid, diethyl terephthalic acid, butantetracarboxylic
acid tetramethylester and butantetracarboxylic acid tetraethylester
as well as mixtures thereof. Other examples include
dimethylisophthalate, diethylisophthalate, dimethylterephthalate or
diethylterephthalate.
The polyoxymethylene can be end capped with a compound having the
general structure of (R.sub.6).sub.qAX.sub.(4-q) wherein
A is an inorganic atom;
q is 1 to 3;
X is a hydrolyzable group such as an alkoxy group (e.g., a C1-C10
alkoxy group), an acyloxy group (e.g., a C1-C10 acyloxy group), a
halogen, etc., and wherein multiple X groups can be the same or
different as one another, at least one of which is an alkoxy group;
and
R.sub.6 is a nonhydrolyzable organic radical.
For example, R.sub.6 can have the general structure of
--(CH.sub.2).sub.s--R.sub.7 wherein
s is 1 to 3; and
R.sub.7 is alkyl (e.g., C1-C10 alkyl), amine, epoxy, mercapto,
vinyl, styryl, aromatic, phosphine, methacrylate, ureido,
polyethylene glycol, organosilane, etc., any of which can include
functional groups, such as halogenated (e.g., fluorinated)
functional groups, and can be branched or straight chained.
By way of example, the end capping compound can be a silane
compound having the general structure of:
(R.sub.6).sub.qSiX.sub.(4-q) Wherein X, q, and R.sub.6 are as
described above.
In one embodiment, the end capping compound can be a dipodal or
tripodal silane compound having the general structure of:
[(R.sub.7)--(CH.sub.2).sub.s].sub.q--SiX.sub.(4-c) wherein X, s and
q are as described above and R.sub.7 is an organosilane compound
having the general structure of
##STR00004## wherein s, q, and X are as defined above and R.sub.8
is alkyl (e.g., C1-C10 alkyl), amine, epoxy, mercapto, vinyl,
styryl, aromatic, phosphine, methacrylate, ureido, polyethylene
glycol, organosilane, etc., any of which can include functional
groups, such as halogenated (e.g., fluorinated) functional groups,
and can be branched or straight chained.
In one embodiment, the nonhydroloyzable organic radical R.sub.6 of
the compound can be a non-reactive radical with no reactive
functionality available on the radical for additional reaction
between the capping agent and other components of the
polyoxymethylene composition. For example, nonhydrolyzable organic
radical can be an alkyl radical. By way of example, the compound
can be an alkoxy silane compound including, without limitation, a
monoalkoxy silane or a dialkoxysilane that includes a C1-C10 alkyl
R.sub.7 group.
In another embodiment, the nonhydrolyzable organic radical can
include reactive functionality such as halogen, vinyl, epoxy,
amino, silane or mercapto functionality, or combinations of
functionality. By way of example, the compound can be a silane
compound such as, but not limited to, chloro-silanes,
vinlyalkoxysilanes, epoxyalkoxysilanes, aminoalkoxysilanes,
mercaptoalkoxysilanes, and combinations thereof. Examples of the
vinylalkoxysilane that may be utilized include
vinyltriethoxysilane, vinyltrimethoxysilane and
vinyltris(.beta.-methoxyethoxy)silane. Examples of the
epoxyalkoxysilanes that may be used include
.gamma.-glycidoxypropyltrimethoxysilane,
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and
.gamma.-glycidoxypropyltriethoxysilane. Examples of the
mercaptoalkoxysilanes that may be employed include
.gamma.-mercaptopropyltrimethoxysilane and
.gamma.-mercaptopropyltriethoxysilane.
Amino silane compounds may be of the formula:
R.sub.9--Si--(R.sub.1D).sub.3, wherein R.sub.9 is selected from the
group consisting of an amino group such as NH.sub.2; an aminoalkyl
of from about 1 to about 10 carbon atoms, or from about 2 to about
5 carbon atoms, such as aminomethyl, aminoethyl, aminopropyl,
aminobutyl, and so forth; an alkene of from about 2 to about 10
carbon atoms, or from about 2 to about 5 carbon atoms, such as
ethylene, propylene, butylene, and so forth; and an alkyne of from
about 2 to about 10 carbon atoms, or from about 2 to about 5 carbon
atoms, such as ethyne, propyne, butyne and so forth; and wherein
R.sub.10 is an alkoxy group of from about 1 to about 10 atoms, or
from about 2 to about 5 carbon atoms, such as methoxy, ethoxy,
propoxy, and so forth.
The compound can generally be provided in a stoichiometric excess,
which can vary depending upon the specific structure of the
polyoxymethylene, e.g., depending upon the content of terminal
hydroxyl groups and/or hemiacetal end groups of the polymer. In
general, the compound can be provided in an amount of less than
about 5 wt. % by weight of the polyoxymethylene polymer, less than
about 1 wt. %, or less than about 0.5 wt. %. For example, the
compound can be provided in an amount of between about 0.05 wt. %
and about 5 wt. %, or between about 0.1 wt. % and about 1 wt.
%.
The end capped polyoxymethylene can be prepared by combination of
the polyoxymethylene and the compound under appropriate conditions
so as to encourage the formation of a covalent bond between a
terminal hydroxyl group end group of the polyoxymethylene and the
compound. A terminal hydroxyl group can be, for example, a portion
of a terminal hemiacetal group or a portion of a terminal
hydroxyalkylene group. In general, the polyoxymethylene and the
compound can be combined in the melt. The reaction of the
components in a reactive processing step is typically effected at
temperatures of from about 100.degree. C. to about 260.degree. C.,
or from about 150.degree. C. to about 220.degree. C., and the
duration of reaction is typically from about 0.2 minutes to about
60 minutes.
A representative reaction scheme for a polyoxymethylene with a
trimethoxy silane compound the is as follows:
##STR00005##
As can be seen, following the reaction, the polymer includes an
inorganic linkage group, in this case a siloxane linking group in
the backbone of the polymer that links the oxymethylene backbone to
the end capping group. This can prevent degradation of the polymer
as well as provide chain extension to the polyoxymethylene and
optionally the addition of a desired reactive functionality to the
terminal ends of the polymer.
A polyoxymethylene composition that incorporates the end capped
polyoxymethylene can include additional additives as are generally
known in the art. For example, in order to further reduce
formaldehyde emissions from the polymeric composition, the
composition can contain a formaldehyde scavenger as is known in the
art, such as a nitrogen containing compound. The addition of a
formaldehyde scavenger to a composition include the end-capped
polyoxymethylene can further reduce the VOC emission level of the
composition. For example, a composition including a high molecular
weight polyoxymethylene (e.g., having a melt flow index of less
than about 5 g/10 min as determined according to ISO 1133 at
190.degree. C. and 2.16 kg, the polyoxymethylene composition can
have a formaldehyde emission Level of less than about 3.0 ppm, less
than about 2.6 ppm, or less than about 1.5 ppm, as determined
according to VDA-275.
The total amount of any formaldehyde scavenger present in the
composition is relatively small. For instance, the formaldehyde
scavenger can be present in an amount less than about 0.5 percent
by weight, such as from about 0.01 percent to about 0.5 percent by
weight, such as from about 0.02 percent to about 0.1 percent by
weight (which excludes other nitrogen containing compounds that may
be present in the composition that are not considered formaldehyde
scavengers such as waxes or hindered amines). Any suitable
formaldehyde scavenger can be included into the composition
including, for example, aminotriazine compounds, allantoin,
hydrazides, polyamides, melamines, or mixtures thereof. In one
embodiment, the formaldehyde scavenger may comprise a heterocyclic
compound having at least one nitrogen atom adjacent to an amino
substituted carbon atom or a carbonyl group. In one specific
embodiment, for instance, the formaldehyde scavenger may comprise
benzoguanamine. In still other embodiments, the formaldehyde
scavenger may comprise a melamine modified phenol, a polyphenol, an
amino acid, a nitrogen containing phosphorus compound, an
acetoacetamide compound, a pyrazole compound, a triazole compound,
a hemiacetal compound, other guanamines, a hydantoin, a urea
including urea derivatives, and the like, as well as combinations
of scavengers.
The polymeric composition can include an acid scavenger that can
prevent acid catalyzed hydrolytic decomposition of the
polyoxymethylene. The inclusion of an acid scavenger may be of
particular benefit at high temperature/high humidity processing
conditions. By way of example, an acid scavenger can include,
without limitation, hydroxides, inorganic acid salts, phosphates,
hydrogen phosphates, and carboxylic acid salts of alkali metals and
alkaline earth metals. Examples can include calcium hydroxide;
magnesium hydroxide; barium hydroxide; lithium, sodium, calcium, or
aluminum (hydroxyl)carbonates such as calcium carbonate, magnesium
carbonate, barium carbonate, calcium silicate, magnesium silicate,
calcium laurate, magnesium laurate, calcium stearate, magnesium
stearate, zinc stearate, calcium behenate, magnesium behenate,
calcium lactate, calcium stearoyl lactylate, zinc oxide, natural
and synthetic hydrotalcites, sodium phosphate, sodium hydrogen
phosphate, and the like. In one embodiment, the acid scavenger can
be a hydroxystearate salt, for instance calcium, magnesium, or zinc
hydroxystearate. Acid scavengers may be used alone or in
combination of two or more when forming the polymeric composition
and this is not critical.
An acid scavenger can generally be included in a polymeric
composition in an amount of from about 0.01 wt. % to about 10 wt.
%, or from about 0.02 wt. % to about 5 wt. %, based on the total
weight of the polymeric composition.
The inclusion of an acid scavenger may be particularly useful in
those embodiments in which the polymeric composition is processed
at high temperatures, for instance greater than about 200.degree.
C., as the addition of the acid scavenger can improve the thermal
stability of the system.
In addition to the above components, the polymeric composition may
contain various other additives and ingredients. For instance, the
composition may contain colorants, light stabilizers, antioxidants,
processing aids, gloss agents, and fillers. For example, in one
embodiment the polymeric composition can include calcium carbonate,
which can improve the color characteristics of the composition.
Colorants that may be used include any desired inorganic pigments,
such as titanium dioxide, ultramarine blue, cobalt blue, and other
organic pigments and dyes, such as phthalocyanines, anthraquinones,
and the like. Other colorants include carbon black or various other
polymer-soluble dyes. The colorants can generally be present in the
composition in an amount up to about 2 percent by weight.
Other additives that may be included in the composition include an
ester of a polyhydric alcohol and at least one fatty acid. The
fatty acid can have from about 10 to about 32 carbon atoms, while
the polyhydric alcohol can have from about 2 to about 8 carbon
atoms. Such alcohols include ethylene glycol, glycerol, butylene
glycol, and pentaerythritol. Fatty acids that may be used include
montanic acids.
Another possible additive is a metal salt of a short-chain
carboxylic acid. The metal used to construct the metal salt, for
instance, may comprise an alkali metal or an alkaline earth metal.
The carboxylic acid may possess from about 3 to about 8 carbon
atoms.
Still another additive that may be present in the composition is a
sterically hindered phenol compound. Examples of such compounds,
which are available commercially, are pentaerythrityl
tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox
1010, BASF), triethylene glycol
bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate] (Irganox
245, BASF),
3,3'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionohydrazide]
(Irganox MD 1024, BASF), hexamethylene glycol
bis[3-(3,5-di-cert-butyl-4-hydroxyphenyl)propionate] (Irganox 259,
BASF), and 3,5-di-tert-butyl-4-hydroxytoluene (Lowinox BHT,
Chemtura). Preference is given to Irganox 1010 and especially
Irganox 245.
Light stabilizers that may be present in the composition include
sterically hindered amines. Such compounds include
2,2,6,6-tetramethyl-4-piperidyl compounds, e.g.,
bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (Tinuvin 770, BASF)
or the polymer of dimethyl succinate and
1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl-4-piperidine
(Tinuvin 622, BASF). UV stabilizers or absorbers that may be
present in the composition include benzophenones or
benzotriazoles.
If desired, the polyoxymethylene composition may also be combined
with a filler material to form a filled composition and to enhance
strength. A filled composition can include, for example, a mineral
filler and/or a fiber filler optionally in conjunction with one or
more other additives as are generally known in the art.
The polyoxymethylene composition may be an unfilled composition. In
another embodiment, however, the composition may include a filler
material. For example, fibers may be employed as a filler material
to improve the mechanical properties of the composition. Such
fibers generally have a high degree of tensile strength relative to
their mass. For example, the ultimate tensile strength of the
fibers (determined in accordance with ASTM D2101) is typically from
about 1,000 to about 15,000 Megapascals ("MPa"), in some
embodiments from about 2,000 MPa to about 10,000 MPa, and in some
embodiments, from about 3,000 MPa to about 6,000 MPa. Fibers may be
formed from materials that are also generally insulative in nature,
such as glass, ceramics (e.g., alumina or silica), aramids (e.g.,
Kevlar.RTM. marketed by E. I. duPont de Nemours, Wilmington, Del.),
polyolefins, polyesters, etc., as well as mixtures thereof. Glass
fibers are particularly suitable, such as E-glass, A-glass,
C-glass, D-glass, AR-glass, R-glass, S1-glass, S2-glass, etc., and
mixtures thereof.
Mineral fillers may be employed as a filler material to improve
mechanical properties. Mineral fillers may, for instance, be
employed in the filled polymer composition to help achieve the
desired mechanical properties and/or appearance. When employed,
mineral fillers typically constitute from about 5 wt. % to about 60
wt. %, in some embodiments from about 10 wt. % to about 55 wt. %,
and in some embodiments, from about 20 wt. % to about 50 wt. % of
the polymer composition. Clay minerals may be particularly suitable
for use in the present invention. Examples of such clay minerals
include, for instance, talc (Mg.sub.3Si.sub.4O.sub.10(OH).sub.2),
halloysite (Al.sub.2Si.sub.2O.sub.5(OH).sub.4), kaolinite
(Al.sub.2Si.sub.2O.sub.5(OH).sub.4), illite
((K,H.sub.3O)(Al,Mg,Fe).sub.2
(Si,Al).sub.4O.sub.10[(OH).sub.2,(H.sub.2O)]), montmorillonite (Na,
Ca).sub.0.33(Al,Mg).sub.2Si.sub.4O.sub.10(OH).sub.2.nH.sub.2O),
vermiculite
((MgFe,Al).sub.3(Al,Si).sub.4O.sub.10(OH).sub.2.4H.sub.2O),
palygorskite ((Mg,Al).sub.2Si.sub.4O.sub.10(OH).4(H.sub.2O)),
pyrophyllite (Al.sub.2Si.sub.4O.sub.10(OH).sub.2), etc., as well as
combinations thereof. In lieu of, or in addition to, clay minerals,
still other mineral fillers may also be employed. For example,
other suitable silicate fillers may also be employed, such as
calcium silicate, aluminum silicate, mica, diatomaceous earth,
wollastonite, and so forth. Mica, for instance, may be particularly
suitable. There are several chemically distinct mica species with
considerable variance in geologic occurrence, but all have
essentially the same crystal structure. As used herein, the term
"mica" is meant to generically include any of these species, such
as muscovite (KAl.sub.2(AlSi.sub.3)O.sub.10(OH).sub.2), biotite
(K(Mg,Fe).sub.3(AlSi.sub.3)O.sub.10(OH).sub.2), phlogopite
(KMg.sub.3(AlSi.sub.3)O.sub.10(OH).sub.2), lepidolite
(K(Li,Al).sub.2-3(AlSi.sub.3)O.sub.10(OH).sub.2), glauconite
(K,Na)(Al,Mg,Fe).sub.2(Si,Al).sub.4O.sub.10(OH).sub.2), etc., as
well as combinations thereof.
The processing of the composition can be effected by mixing the
components and subsequent thermoplastic processing or by mixing the
components in heatable mixing units suitable for this purpose.
Suitable mixing units and mixing processes are described, for
example, in: Saechtling, Kunststoff-Taschenbuch [Plastics
Handbook], Hanser Verlag, 27th edition 1998, on pages 202 to
217.
In one embodiment, the components of the polymeric composition can
be reacted together and compounded prior to being used in a further
molding process for formation of a product. For instance, in one
embodiment, the different components can be melted and mixed
together in a conventional single or twin screw extruder at a
temperature described above. Extruded strands may be produced by
the extruder and then pelletized. Prior to compounding, the polymer
components may be dried to a moisture content of about 0.05 weight
percent or less. If desired, the pelletized compound can be ground
to any suitable particle size, such as in the range of from about
100 microns to about 500 microns.
Shaping processes for forming articles of the polyoxymethylene
composition can include, without limitation, extrusion, injection
molding, blow-molding, compression molding, hot-stamping,
pultrusion, and so forth. Shaped articles that may be formed may
include structural and non-structural shaped parts. For instance,
automotive components such as fuel tanks, and fuel caps, fuel
filler necks, fuel sender unit components (e.g. flanges or swirl
pot), fuel pumps, fuel rails, turn signal and light shifters, power
window components, door lock system components, and so forth can be
formed from the polyoxymethylene composition.
By way of example, in one embodiment, the polyoxymethylene
composition can be utilized to form a container such as a fuel tank
according to a blow molding process. In general, the blow molding
process begins with melting the molding composition and forming it
into a parison. Single screw extruders with the appropriate screw
design are used to convert the composition (usually pellets) into a
homogeneous melt. Depending on the melt strength one can use the
composition with the regular classic extrusion blow molding
process. This applies for the composition with a maximum parison
length of 250 to 300 mm. For larger parison length it might be
necessary to use the extrusion blow molding process with an
additional accumulator head. The size of the head depends on the
amount of material to form a specific container size and wall
thickness.
The basic process has two fundamental phases. Initially, the
parison itself (parison means tube-like piece of plastic) is
extruded vertically out of the die. Once the parison settles on the
injector pin (air injector), the mold is closed. In the second
phase air is injected into the tube and pressure increased until it
reaches the wall of the tool.
The pressure is generally held until the melt solidifies. A
desirable factor for this process is to achieve components with a
homogenous wall thickness distribution throughout the whole
component/parison length. This can be achieved with a wall
thickness control feature (WDS) at the die head. In general this
feature means that a programming step is incorporated into the
process to establish an extrusion/wall thickness profile while the
parison is ejected from the accumulator head.
Of course, any other formation process as is known in the art can
alternatively be utilized in forming the polyoxymethylene
composition. For example, the polyoxymethylene composition can be
shaped according to a rotomolding process to form a hollow product.
Processing by rotomolding typically takes place at oven
temperatures of from about 100.degree. C. to about 300.degree. C.,
or from about 200.degree. C. to about 270.degree. C., and the
processing time is typically from about 1 minute to about 60
minutes, or from about 20 minutes to about 30 minutes.
Furthermore, hollow products formed of the polyoxymethylene
composition can include walls that are composed of layers of
different materials, e.g. an external layer composed of
polyethylene and an internal layer composed of the
polyoxymethylene. The polyoxymethylene composition moreover is
effective in flowing around inserts introduced into the rotomolding
mold during the rotomolding process and integrating them into the
hollow product.
The polyoxymethylene composition can be shaped according to an
injection molding process to form products that can have a
relatively intricate or complicated shape. For example, products
that can be formed from the polyoxymethylene composition that may
be formed according to an injection molding process can include
components such as, without limitation, mechanical gears, sliding
and guiding elements, housing parts, springs, chains, screws, nuts,
fan wheels, pump parts, valve bodies, hardware such as locks,
handles, and hinges, zippers, and so forth.
An injection molding process can generally include heating the
polyoxymethylene molding composition in a preheating zone to a
plastic melt, and thereafter forcing the composition through a
nozzle into a closed mold. Heating of the polyoxymethylene is
typically to a temperature of from about 180.degree. C. to about
240.degree. C. The temperature of the mold is generally
substantially lower, e.g., about 100.degree. C. lower, although the
exact relationship between the melt temperature and the mold
temperature is dependent on factors such as the desired surface
characteristics of the shaped article as will be appreciated by the
skilled artisan. The injection molding may be carried out in
conventional injection-molding apparatus having, for example, a
preheating cylinder, plunger, or reciprocating screw, torpedo,
nozzle and mold including a sprue, runners, gates and mold
cavities. Cylinder temperatures are usually between about
180.degree. C. and about 240.degree. C. and molding pressures are
usually between about 5,000 and 20,000 psi. Actual molding
temperatures and pressures will vary depending on the type of
machine as is known, e.g., employment of a plunger injection
molding machine or a screw injection molding machine or on the
desired shape and size of the molded article. Cycle times are
usually between about 30 and about 110 seconds.
The polyoxymethylene composition can also be utilized in electrical
applications, for instance in forming insulators, bobbins,
connectors, and parts for electronic devices such as televisions,
telephones, etc. Medical devices such as injection pens and metered
dose inhalers can be formed of the polyoxymethylene composition as
well as a variety of sporting goods equipment (e.g., paintball
accessories and airsoft guns) and household appliances (e.g.,
coffee makers and knife handles). The polyoxymethylene composition
can also be utilized in forming automotive components such as,
without limitation, fuel system components (e.g., fuel tanks, fuel
sender units, fuel caps, fuel pumps, etc.), lighting and signal
components, and window and door lock components.
Embodiments of the present disclosure are illustrated by the
following examples that are merely for the purpose of illustration
of embodiments and are not to be regarded as limiting the scope of
the invention or the manner in which it may be practiced. Unless
specifically indicated otherwise, parts and percentages are given
by weight.
Test Methods
Tensile bar formation: A roboshot 110 SiB molding machine was used
to produce tensile bars. Tensile bars are injection molded to ISO
527-1 specifications according to standard ISO conditions.
Temperatures are 177.degree. C., 182.degree. C., 188.degree. C. and
193.degree. C. (rear to nozzle) with a mold temperature of
80.degree. C. and an injection speed of 200 mm/s.
Melt Flow Index: Melt flow index was determined according to ISO
1133 at 190.degree. C. and 2.16 kg load.
Formaldehyde Emission: Plaques of wall thickness 1 mm were
injection molded. After storage for 24 h, formaldehyde emission was
determined according to VDA-275 (German Automotive Industry
Recommendation No. 275, documented by Kraftfahrwesen e.V., July,
1994) (3 hours at 60.degree. C., bottle method). The melt
temperature measured at the die was varied in certain examples as
provided in the results.
Tensile Modulus, Tensile Stress, and Tensile Elongation: Tensile
properties were tested according to ISO Test No. 527 (technically
equivalent to ASTM D638). Modulus and strength measurements were
made on the same test strip sample having a length of 80 mm,
thickness of 10 mm, and width of 4 mm. Testing temperature was
23.degree. C., and testing speed was 50 mm/min.
Flexural Modulus, Flexural Stress, and Flexural Strain: Flexural
properties were tested according to ISO Test No. 178 (technically
equivalent to ASTM D790). This test was performed on a 64 mm
support span. Tests were run on the center portions of uncut ISO
3167 multi-purpose bars. Testing temperature was 23.degree. C., and
testing speed was 2 mm/min.
Notched Charpy Impact Strength: Notched Charpy properties are
tested according to ISO Test No. ISO 179-1 (technically equivalent
to ASTM D256, Method B). This test is run using a Type A notch
(0.25 mm base radius) and Type 1 specimen size (length of 80 mm,
width of 10 mm, and thickness of 4 mm). Specimens are cut from the
center of a multi-purpose bar using a single tooth milling machine.
The testing temperature is 23.degree. C.
Deflection Under Load Temperature ("DTUL"): The deflection under
load temperature was determined in accordance with ISO Test No.
75-2 (technically equivalent to ASTM D648-07). A test strip sample
having a length of 80 mm, thickness of 10 mm, and width of 4 mm was
subjected to an edgewise three-point bending test in which the
specified load (maximum outer fibers stress) was 1.8 MPa. The
specimen was lowered into a silicone oil bath where the temperature
is raised at 2.degree. C. per minute until it deflects 0.25 mm
(0.32 mm for ISO Test No. 75-2).
Color Characteristics: The Hunter scale values, L, a, and b, were
determined according to CIELAB testing methods.
Yellowness Index: The ASTM Yellowness Index for Examples 1-6 was
determined according to ASTM E313, "Standard Practice for
Calculating Yellowness and Whiteness Indices from Instrumentally
Measured Color Coordinates,"
The DIN Yellowness Index for Examples 7-8 was determined by use of
a BYK Gardner Color Sphere spectrophotometer according to DIN 6167
with standard light D 65 and an observation angle of
10.degree..
Percent of Hydrolyzable Groups: A sample was pre-dried and then
hydrolyzed in aqueous triethylamine at 188.degree. C. (under
pressure) for 20 min. The liberated formaldehyde is determined by
the sulfite titration method. This method is used to measure wt. %
hydrolysable portion of polyoxymethylene polymer.
Nuclear Magnetic Resonance (NMR): The sample is added to 0.5 mL
Hexafluoro-isopropanol(HFlP)-d.sub.2 solvent. The .sup.1H NMR
spectrum for the sample was collected on a Bruker Advance III 400
MHz spectrometer (37.degree. C.) using 5 mm DUL probe.
Materials (Examples 1-6)
Silane Compounds:
(3-aminopropyl)triethoxy silane (ATEO) was utilized as an amino
functional silane compound.
(3-mercaptopropyl)trimethoxy silane (MTMO) was utilized as a
mercapto functional silane compound.
Octyl triethoxysilane (OTEO) was utilized as an alkyl silane
compound.
Lubricant: N,N'-ethylene bis-stearamide wax.
Antioxidant:
triethyleneglycol-bis[3-(3-t-butyl-4-hydroxy-5-methyphenyl)propionate
Formaldehyde Scavengers:
a. Benzoguanamine (2,4-Diamino-6-phenyl-1,3,5-triazine).
b. copolyamide
c. 5-ureidohydantoin
Stabilizer: tricalcium citrate acid
Nucleant: an acetal copolymer
Example 1
A mid molecular weight polyoxymethylene, Hostaform.RTM. HS90 (HF
HS90), available from Ticona Engineering Polymers of Florence, Ky.
was utilized to form polyoxymethylene compositions as described in
the table below. The components as described below were mixed in a
Werner Pfleiderer ZSK 32 co-rotating intermeshing twin-screw
extruder with a 32 mm diameter. Samples were molded on a Mannesmann
Demag D100 NCIII injection molding machine.
TABLE-US-00001 Comp. Comp. Inv. Component Sample 1 Sample 2 Sample
1 Lubricant 0.20% 0.20% 0.20% Antioxidant 0.3% 0.3% 0.3%
Benzoguanamine -- 0.5% -- Stabilizer 0.05% 0.05% 0.05% Nucleant
0.50% 0.50% 0.50% MTMO -- -- 0.50% POM 98.95% 98.45% 98.45%
FORMULATION % TOTAL 100.0% 100.0% 100.0%
The compositions and tensile bars formed of the compositions were
tested for a variety of physical characteristics. Results are
provided in the table below:
TABLE-US-00002 Comp. Comp. Inv. Sample 1 Sample 2 Sample 1 Melt
Index (g/10 min) 8.03 8.20 7.94 Tensile Modulus (50 mm/min) (MPa)
3189 3010 3081 Tensile Break Stress (50 mm/min) 69.26 64.91 66.34
(MPa) Tensile Break Strain (50 mm/min) 41.08 49.30 50.20 (%) Yield
strain (%) 13.57 13.59 13.66 Yield stress (Mpa) 73.48 72.58 72.46
Flex Modulus (2 mm/min) (MPa) 2978.00 2797.00 2843.00 Flex Stress
(2 mm/min) (MPa) @ 80.27 74.57 76.30 3.5% Charpy Notched Impact
Strength 7.30 7.80 6.90 (kJ/m.sup.2) DTUL @1.8 Mpa 111.30 107.30
110.50 VDA-275 (ppm) 3.31 2.92 0.36 ASTM Yellowness index -2.67
-0.53 -1.11 L 88.06 87.91 87.03 a 0.56 0.02 0.23 b -1.28 -0.15
-0.25
As can be seen, the addition of the benzoguanamine formaldehyde
scavenger to the composition is not effective in reducing
formaldehyde emission. The addition of the mercapto silane
compound, however, is able to reduce formaldehyde emission by 89%
as compared to the similar composition that does not include the
silane compound.
The percentage of hydrolyzable groups on each sample was
determined. Results are shown in FIG. 1.
Thermogravimetric analysis was also carried out with the three
samples at two different test conditions. In the first run, the
conditions included a ramp-up of 20.degree. C. per minute to
240.degree. C., followed by isothermal conditions at 240.degree. C.
for 60 minutes. Results are shown in FIG. 2. In the second run, the
conditions included a ramp-up of 20.degree. C. per minute to
275.degree. C., followed by isothermal conditions at 275.degree. C.
for 30 minutes. Results are shown in FIG. 3.
Nuclear magnetic resonance end group analysis was carried out on
the samples. Results provided evidence that the mercapto silane
compound is capping the polyoxymethylene at the terminal hydroxyl
groups. Results are provided in the table below:
TABLE-US-00003 OCH.sub.3 C1OH C2OH C2 Formate mmol/ mmol/ mmol/
Sample ID wt % mol % kg kg kg Comparative Sample 1 0.22 0.00 45.61
25.54 12.55 Comparative Sample 2 0.23 0.00 46.49 29.67 10.85
Inventive Sample 1 0.20 0.00 41.86 2.21 9.01
Example 2
A mid molecular weight polyoxymethylene, Celcon.RTM. M90 (CN M90)
available from Ticona Engineering Polymers of Florence, Ky. was
utilized to form polyoxymethylene compositions as described in the
table below. The components as described below were mixed in a
Werner Pfleiderer ZSK 32 co-rotating intermeshing twin-screw
extruder with a 32 mm diameter. Samples were molded on a Mannesmann
Demag D100 NCIII injection molding machine
TABLE-US-00004 Comp. Inv. Inv. Inv. Inv. Inv. Component Sample 3
Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Lubricant 0.20% 0.20%
0.20% 0.20% 0.20% 0.20% Antioxidant 0.3% 0.3% 0.3% 0.3% 0.3% 0.3%
Benzoguanamine 0.5% -- -- -- -- -- Stabilizer 0.05% 0.05% 0.05%
0.05% 0.05% 0.05% Nucleant 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% ATEO
-- 0.50% 0.10% -- -- -- MTMO -- -- -- 0.50% -- -- OTEO -- -- -- --
0.50% 0.10% POM 98.45% 98.45% 98.85% 98.45% 98.45% 98.85%
FORMULATION % TOTAL 100.0% 100.0% 100.0% 100.0% 100.00% 100.00%
The compositions and tensile bars formed of the compositions were
tested for a variety of physical characteristics. Results are
provided in the below table:
TABLE-US-00005 Comp. Inv. Inv. Inv. Inv. Inv. Sample 3 Sample 2
Sample 3 Sample 4 Sample 5 Sample 6 Melt Index (g/10 min) 9.280
9.217 9.190 9.430 9.509 9.260 Tensile Modulus (50 mm/min) (MPa)
2584 2718 2723 2590 2694 2745 Tensile Break Stress (50 mm/min)
(MPa) 52.40 56.91 55.22 52.14 60.62 58.58 Tensile Break Strain (50
mm/min) (%) 34.39 30.93 30.85 34.89 27.57 36.11 Yield strain (%)
10.51 9.75 9.96 10.13 10.45 9.94 Yield stress (MPa) 64.63 65.26
65.33 63.45 63.52 64.56 Flex Modulus (2 mm/min) (MPa) 2363.00
2466.00 2506.00 2383.00 2483.00 2520.00 Flex Stress (2 mm/min)
(MPa) @ 3.5% 65.25 67.75 69.45 66.41 67.91 69.41 Charpy Notched
Impact Strength 6.90 5.60 6.20 6.70 6.00 5.60 (kJ/m.sup.2) DTUL
@1.8 MPa 101.10 98.30 100.60 101.20 103.20 107.10 VDA-275 (ppm)
1.65 1.47 4.32 0.40 1.21 1.82 ASTM Yellowness index -5.52 -5.53
-5.64 -6.34 1.23 0.64 L 88.81 90.20 89.45 90.25 91.94 91.94 a -0.22
-0.46 -0.47 -0.17 -0.58 -0.46 b 0.70 1.07 0.90 -0.11 1.16 0.87
As can be seen, all of the silane compounds were effective in
reducing the formaldehyde emission levels, with the mercapto silane
compound MTMO providing a 75% lower emission level as compared to
the composition that utilized a benzoguanamine scavenger alone.
The percentage of hydrolyzable groups for comparative sample 3 and
inventive sample 4 were determined, Results are shown in FIG.
4.
Photographs of comparative sample 3, inventive sample 4 and
inventive sample 5 were taken after scratching (5000 shots) to
determine the presence of mold deposits on the samples. Comparative
sample 3 is seen in FIGS. 5A and 5B in increasing magnification. No
deposit on the mold surface and ring channel was found, with a
slight mold deposit seen in the ventilation channel. Inventive
sample 4 is seen in FIGS. 6A and 6B in increasing magnification. A
very thin mold deposit was seen in the ring channel and on the mold
surface, but it could not be transferred to IR for identification.
Inventive sample 5 is seen in FIGS. 7A and 7B in increasing
magnification. No mold deposit was found on this sample.
Example 3
A high molecular weight polyoxymethylene, Hostaform.RTM. HS15 (HF
HS15) available from Ticona Engineering Polymers of Florence, Ky.
was utilized to form polyoxymethylene compositions as described in
the table below. The components as described below were mixed in a
Werner Pfleiderer ZSK 32 co-rotating intermeshing twin-screw
extruder with a 32 mm diameter. Samples were molded on a Mannesmann
Demag D100 NCIII injection molding machine.
TABLE-US-00006 Comp. Comp. Inv. Component Sample 4 Sample 5 Sample
7 Lubricant 0.20% 0.20% 0.20% Antioxidant 0.3% 0.3% 0.3%
Benzoguanamine -- 0.5% -- Stabilizer 0.05% 0.05% 0.05% Nucleant
0.50% 0.50% 0.50% MTMO -- -- 0.50% POM 98.95% 98.45% 98.45%
FORMULATION % TOTAL 100.0% 100.0% 100.0%
The compositions and tensile bars formed of the compositions were
tested for a variety of physical characteristics. Results are
provided in the below table:
TABLE-US-00007 Comp. Comp. Inv. Sample 4 Sample 5 Sample 7 Melt
index (g/10 min) 1.410 1.330 1.38 Tensile Modulus (50 mm/min) (MPa)
2845 2690 2737 Tensile Break Stress (50 mm/min) 65.22 60.57 65.27
(MPa) Tensile Break Strain (50 mm/min) 45.17 51.42 69.13 (%) Yield
strain (%) 24.05 22.98 22.89 Yield stress (MPa) 68.88 68.43 69.91
Flex Modulus (2 mm/mm) (MPa) 2694.00 2579.00 2585.00 Flex Stress (2
mm/min) (MPa) @ 73.39 70.20 69.06 3.5% Charpy Notched Impact
Strength 9.60 11.60 10.30 (kJ/m.sup.2) DTUL @1.8 MPa 96.00 97.40
101.10 VDA-275 (ppm) 7.97 11.69 5.15 ASTM Yellowness index -4.83
-4.82 -0.35 L 89.88 90.11 88.37 a -0.09 -0.44 -0.02 b 0.89 1.09
-0.26
As can be seen, the utilization of the benzoguanamine scavenger
actually increased the formaldehyde emission levels as compared to
comparative sample no. 5, while the addition of the silane compound
decreased the formaldehyde emission of the low molecular weight
polyoxymethylene by about 35%.
The percentage of hydrolyzable groups for the samples was
determined. Results are shown in FIG. 8.
Example 4
A high molecular weight polyoxymethylene, Celcon.RTM. HS15 (CN
HS15) available from Ticona Engineering Polymers of Florence, Ky.
was utilized to form polyoxymethylene compositions as described in
the table below. The components as described below were mixed in a
Werner Pfleiderer ZSK 32 co-rotating intermeshing twin-screw
extruder with a 32 mm diameter. Samples were molded on a Mannesmann
Demag D100 NCIII injection molding machine.
TABLE-US-00008 Comp. Inv. Inv. Component Sample 6 Sample 8 Sample 9
Lubricant 0.20% 0.20% 0.20% Antioxidant 0.3% 0.3% 0.3% copolyamide
-- 0.05% -- 5-ureidohydantoin -- -- 0.07% Stabilizer 0.05% 0.05%
0.05% Nucleant 0.50% 0.50% 0.50% MTMO -- 0.50% 0.50% POM 98.95%
98.35% 98.33% FORMULATION % TOTAL 100.0% 100.0% 100.0%
The compositions and tensile bars formed of the compositions were
tested for a variety of physical characteristics. Results are
provided in the below table:
TABLE-US-00009 Comp. Inv. Inv. Sample 6 Sample 8 Sample 9 Melt
Index (g/10 min) 1.159 0.955 1.539 Physical Testing Results 024-001
024-003 024-004 ITC - Modulus (50 mm/min) (MPa) 2864 2765 2760 ITC
- Break Stress (50 mm/min) 70.02 67.77 65.81 (MPa) ITC - Break
Strain (50 mm/min) (%) 38.28 57.19 61.92 Yield strain (%) 27.29
28.05 25.07 Yield stress (MPa) 70.86 69.75 69.81 IPF - Flex Modulus
(2 mm/min) 2832 2776 2698 (MPa) IPF - Flex Stress (2 mm/min) (MPa)
75.46 73.73 71.50 @ 3.5% Charpy Notched (kJ/m.sup.2) 9.20 10.20
9.70 VDA-275 (ppm) 5.46 1.03 1.06 ASTM Yellowness index 3.66 2.59
3.56 L 91.83 92.09 91.99 a -0.15 -0.36 -0.55 b 1.98 1.53 2.14
As can be seen, the combination of the formaldehyde scavenger with
the end capping of the polyoxymethylene with the silane compound
can be used together to provide a very low formaldehyde emission
level for the high molecular weight polyoxymethylene
composition.
Example 5
A high molecular weight polyoxymethylene, Celcon.RTM. M15HP(CN M15)
available from Ticona Engineering Polymers of Florence, Ky. was
utilized to form polyoxymethylene compositions as described in the
table below. The components as described below were mixed in a
Werner Pfleiderer ZSK 32 co-rotating intermeshing twin-screw
extruder with a 32 mm diameter. Samples were molded on a Mannesmann
Demag D100 NCIII injection molding machine.
TABLE-US-00010 Comp. Inv. Inv. Component Sample 7 Sample 10 Sample
11 Lubricant 0.20% 0.20% 0.20% Antioxidant 0.2% 0.2% 0.2%
copolyamide -- 0.05% -- 5-ureidohydantoin 0.07% -- 0.07% Nucleant
0.50% 0.50% 0.50% MTMO -- 0.50% 0.50% POM 99.03% 98.35% 98.33%
FORMULATION % TOTAL 100.0% 100.0% 100.0%
The compositions and tensile bars formed of the compositions were
tested for a variety of physical characteristics. Results are
provided in the below table:
TABLE-US-00011 Comp. Inv. Inv. Sample 7 Sample 10 Sample 11 Melt
Index (g/10 min) 1.962 1.489 1.445 ITC - Modulus (50 mm/min) (MPa)
2745 2664 2688 ITC - Break Stress (50 mm/min) 64.59 66.19 59.70
(MPa) ITC - Break Strain (50 mm/min) (%) 49.36 39.14 65.34 Yield
strain (%) 19.59 22.40 21.23 Yield stress (Mpa) 67.66 68.09 67.79
IPF - Flex Modulus (2 mm/min) 2547.00 2617 2619 (MPa) IPF - Flex
Stress (2 mm/min) (MPa) 69.49 70.21 69.80 @ 3.5% Charpy Notched
(kJ/sq_m) 9.50 10.20 9.60 VDA-275 (ppm) 10.11 1.15 2.57 ASTM
Yellowness index 5.14 0.96 2.31 L 90.78 93.16 92.80 a -0.49 -0.45
-0.58 b 2.91 0.74 1.51
As can be seen, the combination of the formaldehyde scavenger with
the end capping of the polyoxymethylene with the silane compound
can be used together to provide a very low formaldehyde emission
level for the low molecular weight polyoxymethylene
composition.
Example 6
Delrin.RTM. 100, a high viscosity polyoxymethylene homopolymer
available from DuPont.TM. and Tenac.RTM. 3010, a high viscosity
polyoxymethylene homopolymer available from the Asahi Kasei
Chemicals Corporation, were processed in conjunction with a silane
compound. Specifically, the as-purchased polyoxymethylene was melt
processed at either 195.degree. C. or 210.degree.. In one run, the
polyoxymethylene was melt processed in conjunction with 0.5 wt % of
the mercapto silane compound. The compositions were then examined
for determination of formaldehyde emission according to VDE-275.
Compositions and results are provided in the table below:
TABLE-US-00012 Formulation Melt VDA-275 Delrin .RTM. Tenac .RTM.
MTMO total temperature (ppm) Comp. sample 8 100.0% -- -- 100.0%
195.degree. C. 8.55 Comp. sample 9 100.0% -- -- 100.0% 195.degree.
C. 5.89 Comp. sample 10 100.0% -- -- 100.0% 210.degree. C. 20.34
Comp. sample 11 100.0% -- -- 100.0% 210.degree. C. 15.39 Comp.
sample 12 -- 100.0% -- 100.0% 195.degree. C. 2.13 Comp. sample 13
-- 100.0% -- 100.0% 210.degree. C. 4.80 Inv. Sample 12 99.5% --
0.5% 100.0% 195.degree. C. 3.05 Inv. Sample 13 99.5% -- 0.5% 100.0%
195.degree. C. 3.03 Inv. Sample 14 99.5% -- 0.5% 100.0% 210.degree.
C. 6.92 Inv. Sample 15 99.5% -- 0.5% 100.0% 210.degree. C. 8.32
Inv. Sample 16 -- 99.5% 0.5% 100.0% 195.degree. C. 2.67 Inv. Sample
17 -- 99.5% 0.5% 100.0% 210.degree. C. 8.60
Example 7
Materials
Polyoxymethylene (POM): A POM copolymer having a melt index of 9
(at 190.degree. C./2.16 kg) with either 3.4 wt. % dioxolane or 2
wt. % ethylene glycol as comonomer
Silane Compound: (3-mercaptopropyl)trimethoxy silane (MTMO)
Acid Scavenger: Calcium-12 Hydroxystearate
Antioxidant: Ethylene bis(oxyethylene)
bis[.beta.3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate])
Lubricant: Ethylene bis stearamide wax
Stabilizer: tricalcium citrate
Formaldehyde scavenger: Benzoguanamine
(2,4-Diamino-6-phenyl-1,3,5-triazine)
Nucleant: an acetal copolymer
Polymeric compositions were formed as described in the table below.
The components were compounded in a Coperion ZSK 25 extruder at 150
rpm, T=190.degree. C., no vacuum. The throughput rate was 15
kg/hr.
TABLE-US-00013 Inv. Inv. Inv. Comp. Component Sample 18 Sample 19
Sample 20 Sample 14 POM 98.45 98.43 98.43 98.45 Antioxidant 0.30
0.30 0.30 0.30 Lubricant 0.20 0.20 0.20 0.20 Stabilizer 0.05 -- --
0.05 Acid Scavenger -- 0.07 0.07 -- MTMO 0.50 0.50 0.50 --
Formaldehyde -- -- -- 0.50 scavenger Nucleant 0.50 0.50 0.50
0.50
The compositions and tensile bars formed of the compositions were
tested for a variety of physical characteristics. The formaldehyde
emission levels (VDA 275) were tested at various different melt
temperatures (MT) and Gardner Yellow Index were tested at various
different melt temperatures, as shown. Results are provided in the
below table:
TABLE-US-00014 Inv. Inv. Inv. Comp. Sample 18 Sample 19 Sample 20
Sample 14 VDA 275 (ppm) MT = 1.6 3.7 3.7 1.0 185.degree. C. VDA 275
(ppm) MT = 25 4.9 3.8 3.5 205.degree. C. VDA 275 (ppm) MT = 58 9.8
6.2 7.6 220.degree. C. DIN Yellowness index -7.4 -6.6 -5.2 -7.3
(Injection plaque 185.degree. C.) DIN Yellowness index -6.4 -3.1
-0.3 -6.6 (injection plaque 205.degree. C.) DIN Yellowness index
-7.1 -1.5 -1.3 -6.6 (injection plaque 220.degree. C.)
As can be seen, the formaldehyde emission values increased with the
melt temperature. In addition, the substitution of tricalcium
citrate with the hydroxystearate acid scavenger improved the
formaldehyde emission level at higher temperatures. FIG. 9
illustrates the change in formaldehyde emission with temperature
for each sample and FIG. 10 illustrates the change in Gardner
Yellowness Index with temperature for each sample.
Example 8
Materials
Polyoxymethytene (POM): Polyoxymethylene (POM): A POM copolymer
having a melt index of 9 (at 190.degree. C./2.16 kg) with either
3.4 wt. % dioxolane or 2 wt. % ethylene glycol as comonomer
Silane Compound: (3-mercaptopropyl)trimethoxy silane (MTMO)
Acid Scavenger: Calcium-12 Hydroxystearate
Antioxidant: Ethylene bis(oxyethylene)
bis[.beta.-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate])
Lubricant:
a. Ethylene bis stearamide wax
b. stearyl stearate
Formaldehyde scavenger: Benzoguanamine
(2,4-Diamino-6-phenyl-1,3,5-triazine)
Nucleant: an acetal copolymer
Light Stabilizer: N-methylated, oligomeric, high molecular weight
hindered amine light stabilizer
UV light absorber:
2-(2H-benzzotriazol-2-yl)4,6-bis(1-ethyl-1-phenylethylphenol
Filler: calcium carbonate
Tribological Property Improver: low density polyethylene graft
copolymer
Polymeric compositions were formed as described in the table below.
The components were compounded in a Coperion ZSK 25 extruder at 150
rpm, T=.190.degree. C., no vacuum. The throughput rate was 15
kg/hr.
TABLE-US-00015 Comp. Inv. Comp. Inv. Component Sample 15 Sample 21
Sample 16 Sample 22 POM 80.55 80.55 80.55 80.55 Lubricant a 0.18
0.18 0.18 0.18 Formaldehyde 0.5 -- 0.5 -- scavenger MTMO -- 0.5 --
0.5 Antioxidant 0.3 0.3 0.3 0.3 Acid Scavenger 0.07 0.07 0.07 0.07
Light stabilizer 0.5 0.5 0.5 0.5 UV light absorber 0.4 0.4 0.4 0.4
Filler 10 10 10 10 Tribological prop. 5 5 5 5 Imp. Lubricant b 2 2
2 2 Nucleant 0.5 0.5 0.5 0.5
The compositions and tensile bars formed of the compositions were
tested for a variety of physical characteristics. The formaldehyde
emission levels (VDA 275) were tested at various different melt
temperatures (MT). Results are provided in the below table:
TABLE-US-00016 Comp. Inv. Comp. Inv. Sample 15 Sample 21 Sample 16
Sample 22 VDA 275 (ppm) MT = 1.5 1.0 2.3 1.3 185.degree. C. VDA 275
(ppm) MT = 2.2 0.9 4.9 1.6 205.degree. C. VDA 275 (ppm) MT = 5.9
1.3 8.8 2.2 220.degree. C. DIN Yellowness index 13.7 11.4 15.5 12.7
(injection plaque 205.degree. C.)
As can be seen, the addition of the acid scavenger to the
formulations improved the formaldehyde emission at higher melt
temperature in the injection molding. FIG. 11 illustrates the
change in formaldehyde emission with temperature for Comparative
Sample 15 and Inventive Sample 21 and FIG. 12 illustrates the
change in formaldehyde emission with temperature for Comparative
Sample 16 and Inventive Sample 22. It may be noted that the
composition of Inventive Sample 21 and Inventive Sample 22 are the
same, the differences in tested characteristics are understood to
be merely expected variations in experimental results.
While certain representative embodiments and details have been
shown for the purpose of illustrating the subject invention, it
will be apparent to those skilled in this art that various changes
and modifications may be made therein without departing from the
scope of the disclosure.
* * * * *